IPv4 Subnet Calculator

Enter an IPv4 address with a CIDR prefix — for example 192.168.1.10/24 — to see the network address, broadcast address, usable host range, subnet mask, wildcard mask and total host count.

The binary breakdown is shown alongside, because seeing exactly where the mask divides network bits from host bits is usually what makes subnetting click.

How it works

An IPv4 address is 32 bits. The prefix length after the slash says how many of those leading bits identify the network; the rest identify a host within it. A /24 reserves 24 bits for the network and leaves 8 for hosts, which is why it holds 256 addresses.

Within any block, two addresses are not usable as hosts:

• The network address — all host bits zero — names the subnet itself.
• The broadcast address — all host bits one — reaches every host on the subnet at once.

So a /24 gives 256 total addresses but only 254 usable ones. This is the arithmetic behind the familiar sizes: /24 is 254 hosts, /25 is 126, /26 is 62, /27 is 30, /28 is 14.

Two prefixes behave as special cases. A /31 has no room for network and broadcast addresses at all; RFC 3021 permits it on point-to-point links where both addresses are simply used as hosts. A /32 describes exactly one address, which is how you write a single-host route or firewall rule.

The wildcard mask is the bitwise inverse of the subnet mask. It appears in Cisco access lists and some routing protocols, where a 0 bit means "must match" and a 1 bit means "ignore".

Frequently asked questions